Bio/Chem/Phys 10
Genetics
Name
Date
Period
PEDIGREE ANALYSIS I
INTRODUCTION
Geneticists are able to study human inheritance by observing the occurrence of traits in families over several
generations. A pedigree is a diagram that shows the appearance of a particular genetic trait from one generation to
the next in a family tree.
From a pedigree it is possible to gain understanding about dominance, sex-linkage, and other factors involved
in human inheritance.
In this activity you will be analyzing different pedigrees and determining the type of inheritance that the
pedigree represents. A pedigree can be either autosomal (non-sex chromosome) or sex-linked. Each of those may
be dominant or recessive.
From the pedigree you will be able to determine the genotype and of the parents and offspring.
PEDIGREE SYMBOLS AND MEANINGS
Symbol Meaning Symbol Meaning
Symbol
unaffected
male
affected
male
unaffected
female
affected
female
Meaning
marriage
Symbol
Meaning
twins
parents and
children:
1 boy, 1 girl
USING A PEDIGREE
PEDIGREE A: Camptobrachydactyly. Camptobrachydactyly is an inherited condition in which individuals
have extremely malformed hands and feet.
The disorder is a dominant disorder. Use "B" to represent the dominant allele and "b" for the recessive allele.
1. List all of the possible genotypes and phenotypes for Camptobrachydactyly.
Genotype
Phenotype
Homozygous
dominant
Heterozygous
Homozygous
recessive
Bio/Chem/Phys 10
Genetics
Page 1 of 5
Pedigree Analysis I
February 2, 2010
GMZ
Pedigree of a family with Camptobrachydactyly
1
3
2. Is person # 4 a male or female?
5
4
8
2
6
9
7
10
11
___________________
3. Which two people are the grandparents in the family?____________________
4. List the numbers of the people who are affected with the disorder. _________________________
TESTING TO SEE IF THE DISORDER IS AUTOSOMAL DOMINANT
PEDIGREE B: Achondroplasia. Achondroplasia is a type of dwarfism, the long bones do not develop properly,
with the result that the individual is usually quite short, although the trunk and head may approach normal size.
The intelligence of these persons is unaffected and they mature physically and mentally.
Use "A" to represent the dominant allele and "a" for the recessive allele.
Pedigree for a family affected with Achondroplasia
1
3
8
4
2
5
9
6
7
10
5. Circle the set of parents with the same phenotype and their child with a different phenotype.
Bio/Chem/Phys 10
Genetics
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Pedigree Analysis I
February 2, 2010
GMZ
When looking at pedigrees, an indicator that can help you determine if the trait is dominant or recessive is by
finding parents with one phenotype with a child of a different phenotype. The parents in both cases will be
heterozygous and the child will be homozygous recessive. If you find this on a pedigree you can use this
information.
If the disorder is dominant the parents will
have the disorder and the child is normal.
DOMINANT DISORDER
Aa
Aa
Parents genotype: Aa
aa
Child’s genotype: aa
If the disorder is recessive then the parents
will be normal and the child will have the
disorder.
RECESSIVE DISORDER
Aa
Parents genotype: Aa
Aa
aa
Child’s genotype: aa
6. From the pedigree involving Achondroplasia, determine if the disorder is dominant or recessive.
7. On the pedigree on the previous page, label all of the individuals with their genotypes.
PEDIGREE C: Tay-Sachs Disease. Tay-Sachs disease is a condition involving degeneration of the nervous
system, appears at about the sixth month after birth. The degeneration of the optic neurons leads to blindness,
followed by loss of intellectual capabilities, progressive muscular weakness, and paralysis. It is usually lethal by
the age of two or three.
In this pedigree use "T" to represent the dominant allele and "t" for the recessive allele.
1
3
8
4
2
5
9
8. Is Tay Sachs Disease a dominant or recessive disorder?
6
7
10
__________________________
9. Label each individual above with the appropriate genotype.
Bio/Chem/Phys 10
Genetics
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Pedigree Analysis I
February 2, 2010
GMZ
PEDIGREE D: Albinism. In albinism, the formation of melanin, a dark skin pigment, are blocked so that albinos
have extremely light skin and hair. They also have little or no coloration in the iris of the eye, giving their eyes a
pale blue or pink appearance. .
In this pedigree use "A" to represent the dominant allele and "a" for the recessive allele.
1
3
2
4
8
5
7
6
10
9
10. Is albanism a dominant or recessive disorder?
11. Label each individual above with the appropriate genotype.
__________________________
12. When two carriers (heterozygous) reproduce what is the probability that one of their children will be affected?
______ Complete the punnett square to justify your answer.
PEDIGREE E: Huntington's Disease. Huntington's disease is most characterized by jerky, random, and
uncontrollable movements. which include slurring of speech, abnormal facial expressions, difficulties chewing and
swallowing. As the disease progresses, memory deficites tend to appear.
In this pedigree use "H" to represent the dominant allele and "h" for the recessive allele.
1
3
9
4
2
5
10
13. Is Huntington's a dominant or recessive disorder?
7
6
11
12
8
13
__________________________
14. Label each individual above with the appropriate genotype.
Bio/Chem/Phys 10
Genetics
Page 4 of 5
Pedigree Analysis I
February 2, 2010
GMZ